The monerans are distinct from eukaryotic organisms because of the structure and chemistry of their cells. As prokaryotes, they lack the definite nucleus and membrane-bound organelles (specialized cellular parts) of eukaryotic cells. They reproduce principally by transverse binary fission, although transfer of DNA between bacteria is widespread and forms the basis of recombinant DNA technology.

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any of a group of microscopic single-celled organisms that live in enormous numbers in almost every environment on Earth, from deep-sea vents to deep below Earth’s surface to the digestive tracts of humans.

any organism that lacks a distinct nucleus and other organelles due to the absence of internal membranes. Bacteria are among the best-known prokaryotic organisms. The lack of internal membranes in prokaryotes distinguishes them from eukaryotes. The prokaryotic cell membrane is made up of...

any of a group of microscopic single-celled organisms that live in enormous numbers in almost every environment on Earth, from deep-sea vents to deep below Earth’s surface to the digestive tracts of humans.